Problem 68 - Chemistry Matter and Change

Question

Write skeleton equations for these reactions. $$\begin{array}{c}{\text { a. sodium carbonate(s) } \rightarrow} \\ {\text { sodium oxide(s) }+\text { carbon dioxide }(g)}\end{array}$$ $$\begin{array}{l}{\text { b. aluminum(s) }+\text { iodine(s) } \rightarrow \text { aluminum iodide(s) }} \\ {\text { c. iron(II) oxide(s) }+\text { oxygen(g) } \rightarrow \text { iron(III) oxide(s) }}\end{array}$$

Step-by-Step Solution

Answer

a. Na₂CO₃(s) → Na₂O(s) + CO₂(g); b. Al(s) + I₂(s) → AlI₃(s); c. FeO(s) + O₂(g) → Fe₂O₃(s)

Step 1: Write the Reactants and Products for Equation a

For the reaction \( \text{a} \), identify the reactants and products: Sodium carbonate decomposes into sodium oxide and carbon dioxide. This gives the unbalanced formula: \( \text{Na}_2\text{CO}_3 (s) \rightarrow \text{Na}_2\text{O} (s) + \text{CO}_2 (g) \).

Step 2: Verify the Skeleton Equation for Equation a

The skeleton equation for reaction \( \text{a} \) is completed since we have identified the formula for each compound. It is: \( \text{Na}_2\text{CO}_3 (s) \rightarrow \text{Na}_2\text{O} (s) + \text{CO}_2 (g) \). No balancing is required for a skeleton equation.

Step 3: Write the Reactants and Products for Equation b

For reaction \( \text{b} \), identify the reactants and product: Aluminum reacts with iodine to form aluminum iodide. This gives the unbalanced formula: \( \text{Al} (s) + \text{I}_2 (s) \rightarrow \text{AlI}_3 (s) \).

Step 4: Verify the Skeleton Equation for Equation b

The skeleton equation for reaction \( \text{b} \) is completed by identifying the formula for each compound involved. It is: \( \text{Al} (s) + \text{I}_2 (s) \rightarrow \text{AlI}_3 (s) \).

Step 5: Write the Reactants and Products for Equation c

For reaction \( \text{c} \), identify the reactants and the product: Iron(II) oxide combines with oxygen to form iron(III) oxide. This gives the unbalanced formula: \( \text{FeO} (s) + \text{O}_2 (g) \rightarrow \text{Fe}_2\text{O}_3 (s) \).

Step 6: Verify the Skeleton Equation for Equation c

The skeleton equation for reaction \( \text{c} \) is complete upon listing the formula for each compound involved. It is: \( \text{FeO} (s) + \text{O}_2 (g) \rightarrow \text{Fe}_2\text{O}_3 (s) \).

Key Concepts

Skeleton Equations

A skeleton equation is a type of chemical equation where only the chemical formulas of the reactants and products are provided. Unlike balanced equations, skeleton equations do not specify the quantities of substances involved. They offer a "skeleton"—a framework that displays the basic components without detailing their proportions.
In a skeleton equation, you need:

• The correct chemical symbols and formulas for all reactants and products.
• The states of matter for all substances, often indicated with (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution.

Skeleton equations are often the first step toward balancing equations. They give you a basic idea of which chemicals are reacting and what they produce. By showing only the reactants and products, they set the stage for further analysis and balancing.

Reactants and Products

Every chemical reaction involves reactants and products. Reactants are the starting substances that undergo change during a chemical reaction. Products are the new substances formed as a result of the reaction. This distinction is crucial for writing any chemical equation.
When examining reactions:

• Identify the reactants: These are usually found on the left side of a chemical equation.
• Identify the products: These appear on the right side of the equation.
• Use an arrow (→) to separate reactants from products, indicating the direction of the reaction.

Understanding the nature of reactants and products helps in forecasting the outcome of a reaction. For example, if you combine aluminum and iodine, the resulting compound would be aluminum iodide. Recognizing this transformation is essential in predicting reactions and writing equations.

Unbalanced Equations

Unbalanced equations mean that the number of atoms for each element is not the same on both sides of the equation. While skeleton equations showcase the framework of the reaction, balancing them is fundamental for understanding and correctly describing the reaction.
Key points about unbalanced equations:

• They highlight the reactants and products involved but do not adhere to the law of conservation of mass.
• Each elemental atom should eventually have the same count on both sides of the equation once balanced.
• Balancing requires the use of coefficients to ensure that no atoms are lost or gained in the reaction.

Unbalanced equations are a natural step in chemical analysis. They allow for adjustments that will satisfy both the chemical and physical laws guiding the transformation from reactants to products.